The investigators are studying if taking simvastatin and vitamin D together will help prevent episodic migraines. Simvastatin is an FDA approved drug that is typically used to treat high cholesterol and reduce the risk of stroke and heart attack. Vitamin D is a vitamin found in certain foods like some types of fish, and in nutritional supplements. This study is 9 months long. Some people who participate will receive simvastatin and vitamin D, and some people will receive a placebo. A placebo is a "sugar pill" that looks like medication but does not have any active ingredients in it.